1. Field of the Invention
This invention relates to an optical waveguide, and an optical waveguide ferrule to which the optical waveguide is fit, and to an optical connector including these components, which are used in the fields of optical communication and optical information processing.
2. Description of the Related Art
In recent years, with the spread and development of information transmitting means such as the Internet, there has been an increasing demand for large-volume and high-speed data transmissions. Optical fibers capable of transmitting a massive volume of information farther with less transmission loss have been used to transmit a large volume of data at high speed, and a multi-core optical connector has been used to collectively connect a plurality of such optical fibers.
This multi-core optical connector is connected to a multi-core optical fiber connector. Here, optical axes of optical waveguides of the multi-core optical connector need to be aligned respectively with optical axes of optical waveguides of the multi-core optical fiber connector. To achieve this, for example, a method called “active alignment” has been used, in which the multi-core optical connector is moved relative to the multi-core optical fiber connector, through optical waveguides of which light is made to pass, such that the intensity of the light entering the optical waveguides of the multi-core optical connector can be maximized, thereby causing the optical axes of the optical waveguides of the multi-core optical connector to align with the optical axes of the optical waveguides of the multi-core optical fiber connector.
However, this active alignment operation is conducted manually, and therefore the cost is high. To reduce the cost, it is required to simplify this operation or to produce a multi-core optical connector and a multi-core optical fiber connector which requires no special alignment operation.
Therefore, as shown in FIG. 8, a method employing an optical waveguide 108, a connector 112 and an optical fiber connector 120 has been disclosed (see, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 8-248269 (Pages 3 to 4, and FIG. 1), 9-105838 (Page 4, and FIG. 1) and 2001-324631 (Page 4, and FIG. 3)). The optical waveguide 108 has a substrate 102, and also has, on the substrate 102, optical waveguide cores 104 and a clad portion 106 surrounding the optical waveguide cores 104. Positioning grooves 110 (or step portions) are formed respectively at opposite side portions of the optical waveguide 108, and extend parallel to each other in the longitudinal direction of the optical waveguide 108. On the other hand, the connector 112 to which optical waveguides cores 122 are to be connected has convex portions 114 corresponding respectively to the grooves 110 of the optical waveguide 108. The positioning grooves 110 of the optical waveguide 108 are engaged respectively with the convex portions 114 of the connector 112, thereby positioning the optical waveguide cores 104 relative to the connector 112.
Since the grooves 110 extend in the longitudinal direction of the optical waveguide cores 104 as described above, the optical waveguide cores 104 are securely positioned in a direction perpendicular to the longitudinal direction of the optical waveguide cores 104 (i.e., a direction parallel to the width of the optical waveguide). However, the optical waveguide cores 104 are not securely positioned in the longitudinal direction of the optical waveguide cores 104. Therefore, when the connector 112 to which the optical waveguide 108 is connected, is connected to the optical fiber connector 120, the optical waveguide 108 must be positioned relative to the optical fiber connector 120 by making the end surfaces of the optical waveguide cores 104 respectively abut the end surfaces of the optical waveguide cores 122 of the optical fiber connector 120. As a result, the end surfaces of the optical waveguide cores 104 are damaged, and optical connection loss increases.
To solve these problems, a method in which tapering surfaces are formed at an optical waveguide and a connector, and the optical waveguide and the connector are positioned relative to each other using these tapering surfaces has been disclosed (see, for example, JP-A No. 2002-020498 (Page 4, and FIG. 1)). This method described briefly, opposite side surfaces of the optical waveguide in a direction parallel to the width of the optical waveguide are used as positioning surfaces, and the tapering surface slanting relative to a plane parallel to optical waveguide cores is formed at one of the side surfaces. Another tapering surface is also formed at the surface of the connector facing the tapering surface of the optical waveguide. The optical waveguide is inserted into the fitting portion of the connector. When a distal end of the tapering surface of the optical waveguide reaches a distal end of the tapering surface of the connector, the optical waveguide is prevented from further advancing, thereby positioning the optical waveguide relative to the fitting portion of the connector.
In this method, however, in cases where the optical waveguide cores are formed on a silicon substrate, a glass substrate or the like, or the optical waveguide is composed of a polymer compound having an insufficient mechanical strength, the optical waveguide, when inserted into the fitting portion of the connector, may be deflected by reaction force developing during the positioning operation carried out by the use of the tapering surfaces, increasing optical connection loss.
Therefore, there is a need for an optical waveguide ferrule having a small size and a sufficient strength, an optical waveguide to be fit in this ferrule, and an optical connector including these components.